"The gender that you perceive the walker to be affects whether you think they're coming towards you or away," says van der Zwan.

As social creatures, humans depend on understanding what other people around us are doing, he says.

We are able to pick up information such as someone's gender, their emotional state and personality traits, on the basis of how they are moving.

"If I'm walking up to you with my arms up, you can tell by the way I'm moving whether I'm likely to give you a big cuddle or whether I might be going to strike you," says van der Zwan.

This ability means we can avoid aggressive looking people even at a distance.

He says people are also good at telling at a distance if others are coming towards them or moving away, which is why we don't tend to collide with others on a crowded footpath.

But, van der Zwan says, what cues do people use to tell them which direction someone is moving?

Point-light figures

To investigate this question, he used what's known as a digitised "point-light figures".

These are figures made out of points of light, which mark the movement of the major joints, such as the ankles, wrists knees, hips, shoulders and head, based on real live people walking on a treadmill.

The researchers developed 13 point-light figures built on a range of actual males and females.

They showed these figures to 10 study participants, half of which were male and half of which female.

There was an 'extreme female' that walked in the style of a cat walk model and an 'extreme male' walker the researchers dubbed "Arnie".

In between were 11 other walking styles that were less extremely male or female.

"We had really girly girls and really masculine guys and there were some really androgenous ones in the middle," says van der Zwan.

Gender factor

The researchers asked the study participants to identify the gender of the walker and which direction they were moving - towards or away.

When participants identified the walker as male, they thought it was moving towards them, says van der Zwan.

But when the participants identified the walker as female, they thought it was moving away from them.

In the case of an androgenous or gender-neutral walker, observers judged it to be a female about as often as they judge it to be a male, says van der Zwan.

"We saw ambivalence about which way they were facing," he says.

The researchers are investigating why people are more likely to think males are walking towards them, but they think it might have evolved as an early survival strategy.

Males are more dangerous than females and so it's better to assume they are moving towards you to avoid being caught off guard, says van der Zwan.

Van der Zwan says such research could also be useful in building security systems to detect cues for suspicious behaviour.

"Most people coming through an airport terminal will walk in a casual way, but some people will walk in an unnatural way because they're uptight or they're nervous."

"If we understand what these important cues are then we'll be able to build systems for detecting aberrations from normal."